Sensor device, and portable communiction terminal and electronic device using the sensor device

ABSTRACT

A sensor device for detecting a positional relationship between a first member and a second member, includes a first electrode provided on a surface of the first member and supplied with an alternating signal of a first frequency, a second electrode provided on a surface of the second member and supplied with an alternating signal of a second frequency, and a beat detector which detects a beat frequency component corresponding to a difference between the first and second frequencies indicative of the positional relationship between the first member and the second member, when the positional relationship between the first and second members changes to cause the first electrode to approach the second electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 11/858,822,which was filed on Sep. 20, 2007 now U.S. Pat. No. 7,705,611, which isbased upon and claims the benefit of priority from prior Japanese PatentApplication No. 2007-022249, filed Jan. 31, 2007, the entire contents ofboth of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sensor device, and a portablecommunication terminal and electronic device using the sensor device.

2. Description of the Related Art

In recent years, proximity sensors that monitors changes in capacitancehave been proposed as sensors for detecting the proximity of an object(see, for example, International Publication No. 2004/059343). Thesecapacitance detection sensors can detect the proximity of an objectwithout contacting it.

However, conventional proximity sensors as disclosed in InternationalPublication No. 2004/059343 basically detect the proximity of allobjects. Accordingly, they are not suitable for detecting a particulardetection target. For instance, to detect the opening/closing of a lidor door, the proximity of only the lid or door should be detected.Actually, however, conventional sensors detect other objects besides thelid or door.

As described above, it is difficult for conventional proximity sensorsto reliably detect only a particular detection target.

BRIEF SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, there is provided asensor device for detecting a positional relationship between a firstmember and a second member, comprising: a first charge-holding electrodeprovided on a surface of the first member and holding a charge; a secondcharge-holding electrode provided on the surface of the first member andholding a charge differing from the charge held by the firstcharge-holding electrode; a first charge-induced electrode provided on asurface of the second member, the first charge-induced electrode havinga charge induced therein in accordance with the charge held by the firstcharge-holding electrode, when the positional relationship between thefirst and second members changes to cause the first charge-holdingelectrode to approach the first charge-induced electrode; a secondcharge-induced electrode provided on the surface of the second member,the second charge-induced electrode having a charge induced therein inaccordance with the charge held by the second charge-holding electrode,when the positional relationship between the first and second memberschanges to cause the second charge-holding electrode to approach thesecond charge-induced electrode; and a difference detector whichgenerates a difference detection signal when a difference between thecharge induced in the first charge-induced electrode and the chargeinduced in the second charge-induced electrode is greater than a presetvalue.

In accordance with a second aspect of the invention, there is provided asensor device for detecting a positional relationship between a firstsubstrate and a second substrate, comprising: a first charge-holdingelectrode provided on a surface of the first substrate and holding acharge; a second charge-holding electrode provided on the surface of thefirst substrate and holding a charge differing from the charge held bythe first charge-holding electrode; a first charge-induced electrodeprovided on a surface of the second substrate, the first charge-inducedelectrode having a charge induced therein in accordance with the chargeheld by the first charge-holding electrode, when the positionalrelationship between the first and second substrates changes to causethe first charge-holding electrode to approach the first charge-inducedelectrode; a second charge-induced electrode provided on the surface ofthe second substrate, the second charge-induced electrode having acharge induced therein in accordance with the charge held by the secondcharge-holding electrode, when the positional relationship between thefirst and second substrates changes to cause the second charge-holdingelectrode to approach the second charge-induced electrode; and adifference detector which generates a difference detection signal when adifference between the charge induced in the first charge-inducedelectrode and the charge induced in the second charge-induced electrodeis greater than a preset value.

In accordance with a third aspect of the invention, there is provided asensor device for detecting a positional relationship between a firstmember and a second member, comprising: a first electrode provided on asurface of the first member and supplied with an alternating signal of afirst frequency; a second electrode provided on a surface of the secondmember and supplied with an alternating signal of a second frequency;and a beat detector which detects a beat frequency componentcorresponding to a difference between the first and second frequencies,when the positional relationship between the first and second memberschanges to cause the first electrode to approach the second electrode.

In accordance with a fourth aspect of the invention, there is provided asensor device for detecting a positional relationship between a firstsubstrate and a second substrate, comprising: a first electrode providedon a surface of the first substrate and supplied with an alternatingsignal of a first frequency; a second electrode provided on a surface ofthe second substrate and supplied with an alternating signal of a secondfrequency; and a beat detector which detects a beat frequency componentcorresponding to a difference between the first and second frequencies,when the positional relationship between the first and second substrateschanges to cause the first electrode to approach the second electrode.

In accordance with a fifth aspect of the invention, there is provided anelectronic device comprising: a first member and a second member movablerelative to each other; a first charge-holding electrode provided on asurface of the first member and holding a charge; a secondcharge-holding electrode provided on the surface of the first member andholding a charge differing from the charge held by the firstcharge-holding electrode; a first charge-induced electrode provided on asurface of the second member, the first charge-induced electrode havinga charge induced therein in accordance with the charge held by the firstcharge-holding electrode, when the positional relationship between thefirst and second members changes to cause the first charge-holdingelectrode to approach the first charge-induced electrode; a secondcharge-induced electrode provided on the surface of the second member,the second charge-induced electrode having a charge induced therein inaccordance with the charge held by the second charge-holding electrode,when the positional relationship between the first and second memberschanges to cause the second charge-holding electrode to approach thesecond charge-induced electrode; and a difference detector whichgenerates a difference detection signal when a difference between thecharge induced in the first charge-induced electrode and the chargeinduced in the second charge-induced electrode is greater than a presetvalue.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a schematic view illustrating the structure of a sensor deviceaccording to an embodiment of the invention;

FIG. 2 is a circuit diagram illustrating the outline of the circuitry ofthe sensor device of the embodiment;

FIG. 3 is a perspective view illustrating an example in which the sensordevice of the embodiment is applied to a portable communicationterminal;

FIG. 4 is a perspective view illustrating another example in which thesensor device of the embodiment is applied to a portable communicationterminal;

FIG. 5 is a perspective view illustrating yet another example in whichthe sensor device of the embodiment is applied to a portablecommunication terminal;

FIG. 6 is a perspective view illustrating another example in which thesensor device of the embodiment is applied to a portable communicationterminal;

FIG. 7 is a schematic view illustrating a structure employed in theembodiment, in which a plurality of electrodes are arranged;

FIG. 8 is a schematic view illustrating a modification of the electrodearrangement of the sensor device of the embodiment;

FIG. 9 is a block diagram illustrating a circuit example employed in thesensor device of FIG. 8;

FIG. 10 is a schematic view illustrating a modification of the electrodearrangement of the sensor device of the embodiment;

FIG. 11 is a block diagram illustrating a configuration example of acircuit employed in the sensor device of FIG. 10;

FIG. 12 is a circuit diagram illustrating a modification of thecircuitry of the sensor device of the embodiment;

FIG. 13 is a schematic view illustrating a structure example of thesensor device of the embodiment;

FIG. 14 is a schematic view illustrating another structure example ofthe sensor device of the embodiment;

FIG. 15 is a sectional view illustrating yet another structure exampleof the sensor device of the embodiment;

FIG. 16 is a sectional view illustrating another structure example ofthe sensor device of the embodiment;

FIG. 17 is a sectional view illustrating a case where the sensor deviceof the embodiment is used as an angle detection sensor;

FIGS. 18A and 18B are plan views illustrating cases where the sensordevice of the embodiment is used as an angle detection sensor; and

FIG. 19 is a circuit diagram illustrating another structure of thesensor device of the embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention will be described with reference to theaccompanying drawings.

FIG. 1 is a schematic view illustrating the structure of a sensor deviceaccording to an embodiment of the invention. The sensor device of FIG. 1detects the open/closed states of the first and second members 10 and20.

On the first member 10, a first charge-holding electrode 11 and secondcharge-holding electrode 12 are provided adjacent to each other. Thefirst and second charge-holding electrodes 11 and 12 hold differentcharges. For instance, the charges held by the first and secondcharge-holding electrodes 11 and 12 may differ in polarity.Alternatively, the charges may differ in absolute value. The first andsecond charge-holding electrodes 11 and 12 are connected to a powersupply 30 as a charge supply unit for supplying charges to them.

On the second member 20, a first charge-induced electrode 21 and secondcharge-induced electrode 22 are provided adjacent to each other. Whenthe members 10 and 20 are closed, the first charge-holding electrode 11faces the first charge-induced electrode 21 and the secondcharge-holding electrode 12 faces the second charge-induced electrode22. Accordingly, when the members 10 and 20 becomes closed state, thefirst charge-holding electrode 11 is positioned close to the firstcharge-induced electrode 21, and the second charge-holding electrode 12is positioned close to the second charge-induced electrode 22. As aresult, charges corresponding to the charges held by the first andsecond charge-holding electrodes 11 and 12 are induced in the first andsecond charge-induced electrodes 21 and 22, respectively. Accordingly,different charges are induced in the first and second charge-inducedelectrodes 21 and 22.

A difference detector 40 is connected to the first and secondcharge-induced electrodes 21 and 22. When the difference between thecharges induced in the electrodes 21 and 22 is higher than a presetvalue, the difference detector 40 generates a difference detectionsignal. Namely, when the members 10 and 20 are closed, different chargesare induced in the first and second charge-induced electrodes 21 and 22,and the difference between the induced charges is higher than a presetvalue. As a result, the difference detector 40 generates a differencedetection signal. In contrast, when the members 10 and 20 are open, thefirst and second charge-induced electrodes 21 and 22 are out ofinfluence of the first and second charge-holding electrodes 11 and 12,and hence no charges are induced in the first and second charge-inducedelectrodes 21 and 22. Accordingly, the difference detector 40 generatesno difference detection signal.

As described above, in the embodiment, the first and secondcharge-holding electrodes 11 and 12 hold different charges. Therefore,when the members 10 and 20 are closed, different charges are induced inthe first and second charge-induced electrodes 21 and 22. Namely, whenthe first and second charge-holding electrodes 11 and 12 are made toapproach the first and second charge-induced electrodes 21 and 22,respectively in accordance with a change in position between the members10 and 20, different charges can be induced in the first and secondcharge-induced electrodes 21 and 22. Therefore, the open/closed statesof the members 10 and 20 can be reliably detected by detecting thedifference between the induced charges.

When a substance other than the first and second charge-holdingelectrodes 11 and 12 comes close to the first and second charge-inducedelectrodes 21 and 22, the same charge is induced therein and nodifference is detected. Thus, only the approach of the first and secondcharge-holding electrodes 11 and 12 to the first and secondcharge-induced electrodes 21 and 22 can be reliably detected.

Further, the first and second charge-holding electrodes 11 and 12 can bearranged on a single plane, and the first and second charge-inducedelectrodes 21 and 22 can also be arranged on a single plane. Thisenables the open/closed states to be reliably detected withoutincreasing the installation areas of the electrodes.

By virtue of the above structure, only the proximity of a particulardetection target can be reliably detected without using a large complexdevice.

FIG. 2 is a circuit diagram illustrating the outline of the circuitry ofthe sensor device of the embodiment.

As shown in FIG. 2, the first and second charge-induced electrodes 21and 22 are connected to a differential amplifier 41. When the members 10and 20 are open, the difference input to the differential amplifier 41is zero (or substantially zero), the difference signal output from thedifferential amplifier 41 is zero (or substantially zero). In contrast,when the members 10 and 20 are closed, the difference input to thedifferential amplifier 41 is higher than a preset value, and hence thedifference signal output from the differential amplifier 41 is at highlevel.

The difference signal output from the differential amplifier 41 is inputto one input terminal of a comparator 42. A reference voltage Vref isapplied to the other input terminal of the comparator 42. Therefore,when the level of the difference signal output from the differentialamplifier 41 is higher than the reference voltage Vref, the comparator42 generates a difference detection signal. In contrast, when the levelof the difference signal output from the differential amplifier 41 islower than the reference voltage Vref, the comparator 42 generates nodifference detection signal.

As described above, when the state of the members 10 and 20 is shiftedfrom the open state to the closed state, and the level of the differencesignal input to the comparator 42 becomes higher than the referencevoltage Vref, the comparator 42 outputs a difference detection signalindicating that the state of the members 10 and 20 has been shifted tothe closed state.

The distance between the first (second) charge-holding electrode 11 (12)and the first (second) charge-induced electrode 21 (22), assumed whenthe members 10 and 20 are closed, is set depending upon the equipment towhich the sensor is applied. Further, the charge induced in the first(second) charge-induced electrode 21 (22) is varied in accordance withthe distance between the first (second) charge-holding electrode 11 (12)and the first (second) charge-induced electrode 21 (22). Accordingly, itis desirable that the charges held by the first and secondcharge-holding electrodes 11 and 12 be set variable in order to carryout suitable detection for the equipment to which the sensor is applied.Specifically, it is desirable to set the power supply 30 as a variablevoltage power supply. When the charges held by the first and secondcharge-holding electrodes 11 and 12 are set variable, accuratesensitivity adjustment can be realized to thereby enhance the accuracyof detection.

In view of executing accurate sensitivity adjustment, the gain of thedifferential amplifier 41 may be set variable. Further, the referencevoltage Vref may be set variable.

Furthermore, in view of enhancing the accuracy of detection, respectiveamplifier circuits may be provided between the first charge-inducedelectrode 21 and differential amplifier 41 and between the secondcharge-induced electrode 22 and differential amplifier 41.

Although, in the example of FIG. 2, a positive power terminal isconnected to the second charge-holding electrodes 12, and a negativepower terminal is connected to the first charge-holding electrode 11,the positive terminal may be connected to one of the first and secondcharge-holding electrodes 11 and 12, and the other charge-holdingelectrode may be grounded. In this case, the one charge-holdingelectrode is charged with positive electricity, and the othercharge-holding electrode is charged with no electricity. Thus, the firstand second charge-holding electrodes 11 and 12 hold charges of differentabsolute values, which enables accurate difference detection. Thispower-supply structure is employed for devices, such as cellular phones,which do not have a negative power supply.

The comparator 42 is not always necessary. As described above, when themembers 10 and 20 are open, the difference signal output from thedifferential amplifier 41 is zero (or substantially zero). This state istreated as a logical value of “0.” In contrast, when the members 10 and20 are closed, a large difference signal is output from the differentialamplifier 41. This state is treated as a logical value of “1.”

FIGS. 3 to 6 show examples in which the sensor device of the embodimentis applied to a portable communication terminal. The portablecommunication terminal is supposed to be a cellular phone.

In FIGS. 3 to 6, the members 10 and 20 correspond to the upper and lowermembers of the cellular phone, respectively. The charge-holdingelectrodes 11 and 12 are provided in a charge-holding electrodearrangement area 100, and charge-induced electrodes 21 and 22 areprovided in a charge-induced electrode arrangement area 200. Further,respective communication function units are provided in the members 10and 20.

FIG. 3 shows an opening/closing type cellular phone. When the members 10and 20 are moved as indicated by the arrow in FIG. 3 to cause thecharge-holding electrode arrangement area 100 and charge-inducedelectrode arrangement area 200 to approach each other, it is detectedthat the members 10 and 20 are closed.

FIG. 4 shows a slide cellular phone. When the members 10 and 20 are slidas indicated by the arrow in FIG. 4 to cause the charge-holdingelectrode arrangement area 100 and charge-induced electrode arrangementarea 200 to approach each other, it is detected that the members 10 and20 are closed.

FIG. 5 shows a rotary cellular phone. When the members 10 and 20 arerotated relative to each other as indicated by the arrow in FIG. 5 tocause the charge-holding electrode arrangement area 100 andcharge-induced electrode arrangement area 200 to approach each other, itis detected that the members 10 and 20 are closed.

FIG. 6 shows another rotary cellular phone. When the members 10 and 20are rotated relative to each other as indicated by the arrow in FIG. 6to cause the charge-holding electrode arrangement area 100 andcharge-induced electrode arrangement area 200 to approach each other, itis detected that the members 10 and 20 are rotated relative to eachother.

In the example shown in FIG. 1, the sensor comprises the twocharge-holding electrodes 11 and 12 and two charge-induced electrodes 21and 22. However, it may comprise three or more charge-holding electrodesand three or more charge-induced electrodes as shown in FIG. 7. Specificexamples of the structure will be described.

FIGS. 8 and 9 show an example that comprises a plurality of sensor(detection) units shown in FIG. 1, each of the units including the firstand second charge-holding electrodes 11 and 12, first and secondcharge-induced electrodes 21 and 22, and difference detector 40. FIG. 8mainly shows arrangement of electrodes, while FIG. 9 mainly shows acircuit structure.

As shown in FIGS. 8 and 9, one sensor unit is formed of charge-holdingelectrodes 11 a and 12 a, charge-induced electrodes 21 a and 22 a, and adifference detector 40 a. Further, another sensor unit is formed ofcharge-holding electrodes 11 b and 12 b, charge-induced electrodes 21 band 22 b, and a difference detector 40 b. The difference detectors 40 aand 40 b are connected to an output-signal generation unit 50. Examplesof the output-signal generation unit 50 will now be described.

A first example of the output-signal generation unit 50 generates anoutput signal when all difference detectors output difference detectionsignals. Namely, this output-signal generation unit 50 serves as an ANDcircuit. In the example shown in FIGS. 8 and 9, when both the differencedetectors 40 a and 40 b output difference detection signals, the unit 50generates an output signal. This structure can prevent erroneousoperations, and reliably detect proximity of a detection target.

A second example of the output-signal generation unit 50 generates anoutput signal when at least one difference detector outputs a differencedetection signal. Namely, this output-signal generation unit 50 servesas an OR circuit. In the example shown in FIGS. 8 and 9, when at leastone of the difference detectors 40 a and 40 b outputs a differencedetection signal, the unit 50 generates an output signal. With thisstructure, even if one of the detection units cannot perform normaldetection, the sensor as a whole can perform normal detection when theother detection unit can perform normal detection. Accordingly,proximity of a detection target can be reliably detected.

FIGS. 10 and 11 show another example that comprises a plurality ofsensor (detection) units shown in FIG. 1, each of the units includingthe first and second charge-holding electrodes 11 and 12, first andsecond charge-induced electrodes 21 and 22, and difference detector 40.FIG. 10 mainly shows arrangement of electrodes, while FIG. 11 mainlyshows a circuit structure.

As shown in FIGS. 10 and 11, one sensor unit is formed of charge-holdingelectrodes 11 and 12 a, charge-induced electrodes 21 and 22 a, and adifference detector 40 a. Further, another sensor unit is formed ofcharge-holding electrodes 11 and 12 b, charge-induced electrodes 21 and22 b, and a difference detector 40 b. The difference detectors 40 a and40 b are connected to an output-signal generation unit 50. Like theoutput-signal generation unit 50 shown in FIG. 9, the output-signalgeneration unit 50 shown in FIG. 11 cab be made to serve as both an ANDcircuit and OR circuit, and can provide the same advantages as thosedescribed with reference to FIGS. 8 and 9.

FIG. 12 shows a modification of the circuit of the sensor deviceaccording to the embodiment. In this modification, a power supply 30 isan AC power supply, and an integration-type low-pass filter 44 isprovided between the differential amplifier 41 and comparator 42. Thisstructure can effectively eliminate noise components and hence canreliably detect proximity of a detection target.

The charge-holding electrodes 11 and 12 may be formed of electret films.Electrets are polymers permanently charged with static electricity. Theelectrostatic charges include both a plus charge and minus charge, andhence the entire polymer is neutral. Electrets include a film electretand nonwoven fabric electret. The film electret is a polymer filmcharged with plus electricity on one surface, and minus electricity onthe other surface. The polymers include polypropylene (PP),polytetrafluoroethylene (PTFE), 4-fluorinated ethylene-6-fluorinatedpolypropylene copolymer (FEP), etc. The film electret is formed bysubjecting a film to corona discharge. The nonwoven fabric electret isobtained by subjecting nonwoven fabric to corona discharge using avoltage of about minus several tens kV, thereby charging the fabric withplus and minus electricity. Accordingly, the nonwoven fabric electret isneutral as a whole. If charges are beforehand held in these electretfilms, the power supply 30 for supplying charges to the charge-holdingelectrodes 11 and 12 can be omitted, thereby enabling the sensor deviceto be made compact and realizing power saving thereof.

Specific configuration examples of the sensor device of the embodimentwill now be described.

FIG. 13 schematically shows a first configuration example. In thisexample, charge-induced electrodes 21 and 22 and a circuit portion 62formed of an IC are provided on the same substrate 61. That is, thecharge-induced electrodes 21 and 22 and a circuit portion 62 areprovided on the same plane. The circuit portion 62 includes variouscircuits such as a difference detector 41 and comparator 42 (see FIG.2). The charge-induced electrodes 21 and 22 are connected to the circuitportion 62 by wires 63. By thus providing the charge-induced electrodes21 and 22 and circuit portion 62 on the same substrate 61 (i.e., on thesame plane), a compact mount structure is realized. However, ifnecessary, the circuit portion 62 may be provided on another substrate.Further, although FIG. 13 shows mounting of the charge-inducedelectrodes 21 and 22, the charge-holding electrodes 11 and 12 can bemounted in the same way. Namely, the charge-holding electrodes 11 and 12and a circuit portion formed of an IC can be provided on the samesubstrate. These substrates are mounted on the members 10 and 20,whereby the charge-holding electrodes 11 and 12 and charge-inducedelectrodes 21 and 22 are mounted on the surface of the members 10 and20.

FIG. 14 schematically shows a second configuration example. In thisexample, the charge-induced electrodes 21 and 22 cover at least part ofa circuit portion 71 formed of an IC. The circuit portion 71 includesvarious circuits such as a difference detector 41 and comparator 42 (seeFIG. 2). The charge-induced electrodes 21 and 22 are connected to thecircuit portion 71 by wires 72. The circuit portion 71 and wires 72 arecovered with a mold resin 73. Since thus, the charge-induced electrodes21 and 22 cover at least part of the circuit portion 71, the arearequired for mounting can be reduced, thereby enabling a compact mountstructure. The charge-holding electrodes 11 and 12 can be mounted in thesame way as shown in FIG. 14. Namely, the charge-holding electrodes 11and 12 are connected to a circuit portion 74 by wires 75. The circuitportion 74 and wires 75 are covered with a mold resin 76.

Although, in the example of FIG. 14, the charge-holding electrodes 11and 12 and charge-induced electrodes 21 and 22 are provided outside thepackage of the mold resin 73, they may be provided in the package. Inthis case, a more compact mount structure can be realized.

FIG. 15 schematically shows a third configuration example. In thisexample, a charge-induced electrode 84 covers at least part of a circuitportion 82. Specifically, the circuit portion 82 is provided on asubstrate 81 and covered with a mold resin 83. The charge-inducedelectrode 84 is provided by plating on the mold resin 83 (actually, aplurality of charge-induced electrodes 84 are provided). The mold resin83 has a hole formed therein for electrically connecting thecharge-induced electrode 84 to a pad 85 incorporated in the circuitportion 82. Since, in this example, too, the charge-induced electrode 84covers at least part of the circuit portion 82, the required mountingarea can be reduced, and a compact mount structure can be realized. Acharge-holding electrode can also be mounted in the same way as thecharge-induced electrode.

FIG. 16 schematically shows a fourth configuration example. Also in thisexample, a charge-induced electrode 94 covers at least part of a circuitportion 92. Specifically, the circuit portion 92 is provided on asemiconductor substrate (e.g., silicon substrate) 91 by a standardintegrated circuit forming technique, and is covered with an insulatingfilm 93. The charge-induced electrode 94 is provided on the insulatingfilm 93 (actually, a plurality of charge-induced electrodes 94 areprovided). The insulating film 93 has a via hole formed therein, and thecharge-induced electrode 94 is electrically connected to the circuitportion 92 via a conductor 95 provided in the via hole. Since, in thisexample, too, the charge-induced electrode 94 covers at least part ofthe circuit portion 92, the required mounting area can be reduced, and acompact mount structure can be realized. A charge-holding electrode canalso be mounted in the same way as the charge-induced electrode.

In the above-described examples, the sensor device is used for detectingthe opening/closing of a portable communication terminal, such as acellular phone. However, the sensor device can be also used fordetecting the opening/closing of other electronic equipments, such as apersonal computer, refrigerator, oven range and door.

FIGS. 17, 18A and 18B show a case where the sensor device of theembodiment is used as an angle detection sensor. FIG. 17 is a crosssectional view of the sensor, and FIGS. 18A and 18B are plan views ofthe same.

As shown in FIGS. 17 and 18A, charge-holding electrodes 11 and 12 arearranged in pairs on the first member 10 between both ends thereof.Similarly, as shown in FIGS. 17 and 18B, charge-induced electrodes 21and 22 are arranged in pairs on the second member 20 between both endsthereof. Further, an end of the first member 10 is connected to an endof the second member 20. The first and second members 10 and 20 canangularly move relative to each other about a connection point Ptherebetween, as is indicated by the arrow in FIG. 17.

As can be understood from FIGS. 17, 18A and 18B, as the angle θ betweenthe members 10 and 20 is decreased, the number of pairs (21, 22) ofinduced electrodes that are turned on (proximity detection state) isincreased. Accordingly, if the relationship between the on/off states ofeach pair (21, 22) of induced electrodes and the angle θ is obtainedbeforehand, the angle θ can be determined from the on/off states of eachpair (21, 22) of induced electrodes. This means that variations in theangle θ can be measured in an analog fashion if the number of pairs ofcharge-holding electrodes (11, 12) and charge-induced electrodes (21 and22) is increased. As a result, an angle detector of a simple structurecan be realized.

FIG. 19 shows another structure of the sensor device according to theembodiment.

The sensor device of FIG. 19 also detects the positional relationship(e.g., opening/closing states) between a first member (corresponding tothe member 10 shown in, for example, FIGS. 1 and 3-6), and a secondmember (corresponding to the member 20 shown in, for example, FIGS. 1and 3-6).

A first electrode 311 is provided on the surface of the first member,and a second electrode 312 is provided on the surface of the secondmember. An AC signal having a first frequency f1 is supplied from afirst AC signal generator 321 to the first electrode 311. An AC signalhaving a second frequency f2 is supplied from a second AC signalgenerator 322 to the second electrode 312. The difference between thefirst and second frequencies f1 and f2 is sufficiently smaller than eachof the frequencies f1 and f2. RI denotes an input resistance, and RGdenotes a floating resistance.

When the first and second members are closed, the first and secondelectrodes 311 and 312 approach each other. As a result, a beatcorresponding to the difference between the first and second frequenciesf1 and f2 occurs. The beat frequency component is detected by a beatdetector 340. The beat detector 340 comprises a low-pass filter (LPF)341 and comparator 342. Namely, the LPF 341 extracts a beat frequencycomponent. The comparator 342 compares the level of the beat frequencycomponent extracted by the LPF 341 with a reference voltage, and outputsa beat detection signal if the former exceeds the latter.

As described above, in the above structure, a beat occurs when the firstand second electrodes 311 and 312 approach each other in accordance witha change in the positional relationship between the first and secondmembers. Accordingly, the positional relationship (e.g., opening/closingstates) between the first and second members can be reliably detected bydetecting a beat frequency component by the beat detector 340.

Further, since the detected beat frequency component corresponds to thedifference between the first and second frequencies f1 and f2, only theproximity of the first and second electrodes 311 and 312 can be reliablydetected. This enables a sensor device simple in structure to reliablydetect only the proximity of a particular detection target.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A sensor device for detecting a positional relationship between afirst member and a second member, comprising: a first electrode providedon a surface of the first member and supplied with an alternating signalof a first frequency; a second electrode provided on a surface of thesecond member and supplied with an alternating signal of a secondfrequency; and a beat detector which detects a beat frequency componentcorresponding to a difference between the first and second frequencies,when the positional relationship between the first and second memberschanges to cause the first electrode to approach the second electrode.2. The device according to claim 1, wherein the beat detector comprisesa low-pass filter that extracts the beat frequency component and acomparator that compares a level of the beat frequency component with areference voltage and outputs a beat detection signal indicative of thepositional relationship between the first member and the second memberif the level of the beat frequency component exceeds the referencevoltage.
 3. A sensor device for detecting a positional relationshipbetween a first substrate and a second substrate, comprising: a firstelectrode provided on a surface of the first substrate and supplied withan alternating signal of a first frequency; a second electrode providedon a surface of the second substrate and supplied with an alternatingsignal of a second frequency; and a beat detector which detects a beatfrequency component corresponding to a difference between the first andsecond frequencies, when the positional relationship between the firstand second substrates changes to cause the first electrode to approachthe second electrode.
 4. The device according to claim 3, wherein thebeat detector comprises a low-pass filter that extracts the beatfrequency component and a comparator that compares a level of the beatfrequency component with a reference voltage and outputs a beatdetection signal indicative of the positional relationship between thefirst member and the second member if the level of the beat frequencycomponent exceeds the reference voltage.